The present invention relates to radiation curable silicon containing polyacrylate hardcoat compositions, method for making, and composites made therefrom. More particularly, the present invention relates to the employment of an anaerobic gelation inhibitor during the devolatilizing of organic solvent from a silicon containing polyacrylate hardcoat mixture to produce a hardcoat composition and the radiation cure of the devolatized product on an organic substrate.
As shown by Chung, U.S. Pat. No. 4,478,876, a process is provided for applying a curable silicon containing polyacrylate hardcoat composition onto a substrate, such as a thermoplastic substrate. The cure of the Chung silicon hardcoat composition is effected in a non-inert atmosphere, such as air.
Chung further shows that a radiation curable silicon containing polyacrylate hardcoat composition, can be made by initially treating aqueous colloidal silica with an alkoxysilylacrylate, such as methylacryloxypropyltrimethoxysilane. Water is then removed from the mixture in the form of an aqueous/organic solvent azeotrope. Prior to devolatilizing, a polyfunctional reactive acrylic monomer, for example hexanedioldiacrylate, can be added to the mixture to provide an acrylic matrix for the silylated colloidal silica upon cure. As taught by Chung, application of the silicon containing polyacrylate hardcoat composition onto a solid substrate such as polycarbonate can provide a composite having improved abrasion resistance. Experience has shown however that premature gelation of reactive acrylic monomer can occur during the devolatilizing step unless unless an inhibitor is used. Accordingly, an inhibitor such as methylhydroquinone (MEHQ) is often employed with some degree of success. Although satisfactory silicon containing polyacrylate hardcoat composites can be made using prior art procedures employing MEHQ as an inhibitor, further improvments in radiation curable silicon containing polyacrylate hardcoat compositions are constantly being sought.